This document relates to a switch having a Hall Effect device, and more particularly to a multi-position switch having a single Hall Effect device with dual digital outputs.
Switches designed to be used in harsh environments are becoming smaller while reliability requirements are simultaneously increasing. For example, switches used in automotive applications, such as gear shifts, would ideally be designed to fit into an isolated area while still maintaining a high reliability as replacing the switch may require significant effort and resources. If the gear shift switch is located in the steering console of an automobile, the entire steering column may need to be removed or replaced to repair the defective switch. Therefore, it is desirable to manufacture reliable compact switches for certain applications.
One possible solution is to manufacture a mechanical switch having various moving parts used to switch between various states. A mechanical switch has several drawbacks. One major drawback is the limited life cycle of the moving parts. Another drawback is that mechanical switches are not as robust against extreme environmental conditions. Mechanical switches require a sealed casing to protect against environmental conditions such as dirt and precipitation. Similarly, the moving pieces may be constructed of various metals (e.g., aluminum, steel) that may react differently in different temperatures. This may result in reduced reliability of the switch as in various temperatures due to changes in materials (e.g., shrinkage or expansion) that may cause reduced contact force in the switch. As discussed above, replacing some switches is tedious and time-consuming, making mechanical switches, with the various drawbacks discussed herein, a less than ideal solution.
Another solution for increasing reliability in switches is using a solid state compact switch utilizing few, if any, moving parts. One example of a solid state switch is a switch utilizing Hall Effect sensors. Hall Effect sensors are specialized integrated circuits which respond to the presence of a magnetic field. By including Hall Effect sensors along with a magnet positioned to move along the Hall Effect sensors, a switch may be constructed that includes a single moving part.
An example of a switch using a Hall Effect sensor is shown in FIG. 1. Specifically, FIG. 1 illustrates switch 100. Switch 100 uses a side approach for the magnet orientation and movement. Switch 100 includes two Hall Effect sensors 102a and 102b. Each Hall Effect sensor includes plates 104a and 104b that are sensitive to a certain magnetic pole. In this example, both sensitive plate 104a of sensor 102a and sensitive plate 104b are sensitive to the south pole of magnet 106. Magnet 106 is configured to move in the direct of the arrow next to sensors 102a and 102b. As the magnet moves toward sensor 102a, plate 104a detects the south pole of magnet 106 and sensor 102a turns on. Similarly, as magnet 106 moves toward sensor 102b, plate 104b detects the south pole of magnet 106 and sensor 102b turns on. The components of switch 100 are configured and arranged such that there are three possible scenarios: (1) when magnet 106 is moved toward sensor 102a, only sensor 102a turns on, (2) when magnet 106 is moved toward sensor 102b, only sensor 102b turns on, and (3) when magnet 106 is in the central or neutral position, both sensors 102a and 102b are off.
Switches using solid state devices like Hall Effect sensors are more reliable than mechanical solutions as the number of moving parts is greatly reduced. Switches using these typical arrangements of Hall Effect sensors, however, still have several drawbacks. One major drawback is that only a single output is available per Hall Effect sensor requiring two Hall Effect sensors be used. Another drawback of these typical arrangements using Hall Effect sensors is switch point tolerance. The switch point tolerance is influenced by a number of factors, including temperature, positional tolerance of the magnet with respect to the Hall Effect sensor in the direction of travel of the magnet, manufacturing variations in the magnet and variation in the Hall Effect sensor operate/release threshold. The strength of the magnet must be carefully matched with the sensitivity of the Hall Effect sensor. If the sensitivity of the Hall Effect sensor is too high with respect to the magnet strength, then positional tolerances may be poor. A higher sensitivity Hall Effect sensor also raises the risk of interference from outside magnetic fields. Conversely, if the sensitivity of the Hall Effect sensor is too low with respect to the magnet strength, the positional tolerance is improved but there is a higher risk that the magnet will not trigger the Hall Effect device.
Due to potentially large positional tolerances, the size of the movements of the magnet from one position to another must be big enough to ensure that there is no overlap in magnetic field detection at the Hall Effect sensor between positions. This large neutral distance between positions is not always desired due to size constraints in certain applications.
Another drawback is the size required to house multiple Hall Effect sensors along with the magnet as well as the addition of another component and the increased likelihood that the component may fail.
Several attempts have been made to overcome the drawbacks of switches using multiple Hall Effect sensors. One example is to use a multi-pole magnet to improve positional tolerance. In the example of switch 100 of FIG. 1, magnet 106 would be replaced with a multi-pole magnet having a north-south-north pole configuration. The multi-pole magnet would create a sharper change in the magnetic field around the switching positions of the magnet's movement, improving the positional tolerance. However, the multi-pole magnet would need to be larger than the standard dipole magnet, making the switch more difficult to package. Also, the multi-pole magnet is more difficult to manufacture than a dipole magnet, resulting in a cost increase.
Another example of a switch providing multiple outputs with a single Hall Effect sensor and magnet utilizes a programmable linear Hall Effect sensor. A programmable linear sensor can be programmed to produce different outputs based on the detected strength of a magnetic field, i.e., as the magnet gets closer, the field increases and changes the output of the sensor. This approach introduces a new set of drawbacks, primarily the need to program the sensors, comparator circuits must be used to interpret the output of the sensor and determine the position of the magnet, and the programmable sensors are significantly more expensive than standard Hall Effect sensors.